The use of thermally expandable microcapsules for increasing the toughness and heal structural adhesives

Guillaume Pesquet,Chiaki Sato,Lucas F M Da Silva

doi:10.3221/igf-esis.16.02

Abstract

In this research, the effect of thermally expandable microcapsules (TEMs) on mode I fracture toughness of structural adhesives were investigated. The single-edge-notch bending (SENB) test was used. Firstly, a standard toughness test was performed on adhesives with microcapsules. Secondly, since TEMs start their expansion at approximately 60ºC, the next specimens were fatigue tested expecting a local heating in the notch leading to the desired expansion before being statically loaded for fracture toughness determination. Thirdly, a manual local heating at 90ºC was applied in the notch before the fracture static test. The experimental results were successfully cross-checked through a numerical analysis using the virtual crack closure technique (VCCT) based on linear elastic fracture mechanics (LEFM). The major conclusion is that fracture toughness of the modified adhesives increased as the mass fraction of the TEMs increased.

Highlights

Expandable microcapsules, thermally expansive particles, thermo-expandable microsphere (TEMs), or a combination of these words, are all particles made up of a thermoplastic shell filled with liquid hydrocarbon
An adhesive joint between metallic adherends such as the double cantilever beam (DCB) test defined in standard ASTM D3433 was not considered because of the high conductivity of metals
When adhesives without thermally expandable microcapsules (TEMs) are heated, they should merely expand according to their volumetric thermal expansion ratio coefficient and contract to the original shape when naturally cooling

Summary

Introduction

Expandable microcapsules, thermally expansive particles, thermo-expandable microsphere (TEMs), or a combination of these words, are all particles made up of a thermoplastic shell filled with liquid hydrocarbon. If it is not the case, i.e. the Tg of the resin is higher than the temperature of expansion of the TEMs, the joint cannot be dismantled. The Tg of the resin is much higher than the temperature of expansion of the TEMs and the strength of the adhesive does not permit the expansion of the particles.

Results

Conclusion